An important constrain in the power production in wind turbines is that imposed by the noise generated during operation. In particular, wind turbine blades produce aerodynamic audible noise due to the interaction between the boundary layer and the trailing edge.
Turbulent boundary layers on wind turbine blades produce noise after the onset of the transition and when interacting with the trailing edge. The anisotropy, history and length scale of the turbulence within the boundary layer affect the noise generated by an airfoil.
There are known several proposals for reducing the aerodynamic noise produced by wind turbine blades.
One of them is the use of serrated trailing edges. In this respect, EP0652367 discloses rotor blades having its rear edge irregularly formed, in particular in a saw-tooth form. EP1314885 discloses rotor blades with serrated trailing edges each having a plurality of span-wise, periodic indentations, in the form a saw teeth having approximately 60 degrees included angles between adjacent vertices. EP1338793 discloses rotor blades in which a dentation is formed in the trailing edge part of the blade which is shaped in a serration of triangular tooth, of trapezoid tooth, or of sawtooth.
Another proposal, disclosed in WO2006/122547, is the use of turbulence generating means as noise reduction means. Said means are placed on the leeward surface side of the wind turbine blade and at the outer section of the wind turbine blade in direction of the blade tip.
The prior art also teaches the use of wind turbine operational control methods for reducing the aerodynamic noise and, in particular, controlling the rotor speed. In this respect, the publication “Wind Turbine Noise”, Wagner et al., Springer-Verlag Berlin Heidelberg 1996 summarizes the problems raised by the noise produced by wind turbines and some proposals for its reduction.
The present invention provides a different solution for reducing the aerodynamic noise produced by the wind turbine blades.